In 1.16, Mojang added ruined portals to vanilla Minecraft:

My proposal is to remake the "Broken Nether Portals" feature to use those structures instead. Of course, blocks that still doesn't exist on 1.12, like Crying Obsidian, can be ignored (or pulled from other mods that adds them, like Future MC, if installed), and basalt, if the proposal of #23 gets done, can be used on the Nether ruined ones.